1. Field of the Invention
The present invention relates to a nitride semiconductor device using group III nitride semiconductors and a method for producing the same.
2. Description of Related Art
Conventionally, a power device using a silicon semiconductor is employed for a power amplifier circuit, a power supply circuit, a motor driving circuit or the like.
However, improvement in withstand voltage, reduction in resistance and improvement in speed of a silicon devices are now reaching the limits due to the theoretical limit of the silicon semiconductor, and it is becoming difficult to satisfy requirements of the market.
Therefore, development of a nitride semiconductor device having characteristics such as a high withstand voltage, a high-temperature operation, a high current density, high-speed switching and small on-resistance is examined.
FIG. 5 is a schematic sectional view for illustrating the structure of a conventional nitride semiconductor device.
This nitride semiconductor device includes a substrate 81 and a multilayer structure portion 93 laminated on the substrate 81.
The multilayer structure portion 93 includes an undoped GaN layer 82, an n-type GaN layer 83, a p-type GaN layer 84 and an n-type GaN layer 85 successively laminated from the side of the substrate 81. Wall surfaces 91 extending over the n-type GaN layer 83, the p-type GaN layer 84 and the n-type GaN layer 85 are formed in the multilayer structure portion 93. A gate insulating film 86 covering the overall regions of the wall surfaces 91 is formed on the surface of the multilayer structure portion 93.
Openings 94 and 92 partially exposing the n-type GaN layers 85 and 83 respectively are formed in the gate insulating film 86.
A source electrode 88 is electrically connected to the portion of the n-type GaN layer 85 exposed from the opening 94. On the other hand, drain electrodes 89 are electrically connected to the portions of the n-type GaN layer 83 exposed from the openings 92. Gate electrodes 87 are formed on portions of the gate insulating film 86 opposed to the wall surfaces 91.
Interlayer dielectric films 90 are interposed between the adjacent ones of the source electrode 88, the drain electrodes 89 and the gate electrodes 87, to isolate these electrodes from one another.
The operation of the nitride semiconductor device is now described. First, a bias (reverse bias) positive on the side of the drain electrodes 89 is supplied between the source electrode 88 and the drain electrodes 89 (the source and the drain), for example. Thus, a reverse voltage is supplied to the interface (p-n junction) between the n-type GaN layer 83 and the p-type GaN layer 84, whereby the n-type GaN layer 85 and the n-type GaN layer 83, i.e., the source and the drain are cut off (reverse-biased).
When a bias exceeding a gate threshold voltage positive with reference to the potential of the source electrode 88 is applied to the gate electrodes 87 in this state, electrons are induced in portions (channel regions) of the p-type GaN layer 84 around the interfaces between the wall surfaces 91 and the gate insulating film 86, to form inversion layers (channels). The source and the drain conduct through the inversion layers.